Friedmann–Einstein Universe: Einstein's Shift to a Dynamic Cosmos
In 1931, Albert Einstein published a model of the universe that marked a pivotal moment in the history of science. Known as the Friedmann–Einstein universe, this model represented the first time Einstein officially embraced the possibility of a cosmos with a time-varying radius, moving away from his previous insistence on a static universe.
The Transition to Dynamic Cosmology
For years, Einstein had favored a static model of the universe. However, the discovery by Edwin Hubble revealed a linear relation between the redshifts (the stretching of light toward longer wavelengths as objects move away) of galaxies and their radial distance. This evidence strongly suggested that the universe was expanding.
Influenced by these findings, Einstein adopted the dynamic cosmology proposed by Alexander Friedmann. To achieve this, Einstein removed the cosmological constant—a term he had previously introduced to maintain a static universe—arguing that it was both unnecessary and unsatisfactory. The resulting model described a universe that expands and subsequently contracts.
Mathematical Foundations and Calculations
Using the Friedmann equations, Einstein derived expressions to relate the density of matter, the radius of the universe, and the duration of the expansion to the Hubble constant (the unit of measurement used to describe the expansion rate of the universe).
Based on the contemporaneous Hubble constant value of 500 km·sMpc, Einstein calculated the following values for his model:
- Density of matter: 10 cm
- Radius of the universe: 10 light-years
- Timespan of expansion: 10 years
Modern analysis has since revealed that these specific calculations contained a slight systematic error.
Einstein's Blackboard and the Oxford Lectures
In May 1931, Einstein presented the Friedmann–Einstein universe during his second Rhodes lecture at Oxford University. The physical blackboard he used during this presentation, now known as Einstein's Blackboard, is preserved at the Museum of the History of Science in Oxford.
Researchers have suggested that the origins of the numerical errors found in the Friedmann–Einstein model may be visible on the preserved blackboard.
Key Facts
- Published: 1931 by Albert Einstein.
- Core Concept: A dynamic universe that expands and then contracts.
- Key Influence: Edwin Hubble's observation of galactic redshifts and Alexander Friedmann's cosmology.
- Major Change: The removal of the cosmological constant from the Friedmann equations.
- Historical Artifact: Einstein's Blackboard at the Museum of the History of Science, Oxford.
| Parameter | Einstein's 1931 Calculated Value | Basis/Constant Used |
|---|---|---|
| Hubble Constant | 500 km·sMpc | Contemporaneous value |
| Density of Matter | 10 cm | Derived from Friedmann equations |
| Universe Radius | 10 light-years | Derived from Friedmann equations |
| Expansion Timespan | 10 years | Derived from Friedmann equations |
Frequently Asked Questions
What is the Friedmann–Einstein universe?
It is a cosmological model published by Albert Einstein in 1931 that describes a universe with a time-varying radius, specifically one that expands and then contracts.
Why did Einstein change his view on a static universe?
Einstein changed his view after Edwin Hubble discovered a linear relationship between the redshifts of galaxies and their distance, which provided evidence that the universe was expanding.
What role did Alexander Friedmann play in this model?
Einstein embraced the dynamic cosmology developed by Alexander Friedmann and utilized the Friedmann equations to derive his model.
What was the significance of the cosmological constant in this model?
Einstein removed the cosmological constant from his equations because he found it unsatisfactory and unnecessary for a dynamic, expanding-contracting model.
Where can Einstein's Blackboard be seen today?
Einstein's Blackboard, used during his 1931 Rhodes lecture at Oxford University, is currently preserved at the Museum of the History of Science in Oxford.